In staggercasting, audio and/or video content is encoded and sent twice in different times, once as a main or base stream and also as a staggercast stream. The staggercast stream is sent in advance compared to the base stream, i.e., the base stream is delayed (with the staggercast delay). An illustrative staggercasting transmitter is shown in FIG. 1. The elements shown in FIG. 1 are well-known and will not be described in detail. In FIG. 1, a staggercast transmitter 100 illustratively comprises a first encoder 101 and a second encoder 102, a staggercast delay 103, a multiplexer (mux) 104, and a modulator 105.
In FIG. 1, audio and/or video content 110 is applied to inputs of encoders 101 and 102, which encode the input signal 110 to provide respectively encoded signals 111 and 112 at the outputs of the encoders 101 and 102. The first encoded signal 111 represents the staggercast stream. The second encoded signal 112 encoded by the second encoder 102 in FIG. 1 is then delayed in time by the staggercast delay 103 to provide the base or main stream 122. The staggercast delay 103 may be adjustable or fixed. As a result of the base stream 122 being delayed by the staggercast delay 103, the staggercast stream 111 is now “in advance” of the base stream 122. Mux 104 then multiplexes the base stream 122 and the staggercast stream 111 to provide an output data packet stream 123 which is subject to further signal modulation (e.g., OFDM, VSB modulation, and etc.) by a modulator 105 as needed. The output 124 of the modulator 105 is then transmitted via a transmission medium (e.g., cellular, broadcast, satellite, cable, Internet, and etc.) to a receiver as a transmitted stream. Also, the encoders 101 and 102 in FIG. 1 may perform the same type of encoding, although this is not required. That is, one encoder may perform the encoding with different modulation formats, coding rate and/or encoding standard than the other. For example, encoder 101 may be more robust and may produce an encoded stream 111 which is more error resistant than the encoded stream 112 produced by the encoder 102, and/or that encoder 101 may produce an audio stream in MP3, and encoder 102 may produce another audio stream in ACC, or vice versa.
Turning now to FIG. 2, an illustrative staggercast receiver 200 is shown. The staggercast receiver 200 comprises a demodulator 201, a demultiplexer (demux) 202, a staggercast stream selector 203 and a decoder 204. The transmitted stream 210 is first received and processed by the demodulator 201. The demodulator 201 demodulates the received RF signal and provides a demodulated output signal 221 to the demux 202. The demux 202 demultiplexes the demodulated signal 221 and provides at its outputs the staggercast stream 211 and the base or main stream 222 which have been multiplexed e.g., at the staggercast transmitter 100 shown in FIG. 1. Therefore, in case of the loss or the degradation of the transmitted stream 210 due to physical disruptions such as e.g., multipath interference or fading, a correction may be made on the receiver side.
The correction may be made, e.g., by the staggercast selector 203 using data from the staggercast stream 211 to replace, supplement or otherwise recover the degraded data in the base stream 222. For example, if the receiver 200 detects degradation in the base or main stream 222, the staggercast selector 203 may select the corresponding data packets from the staggercast stream 211 for the degraded data packets in the base stream 222, since the base stream 222 has been delayed by the staggercast delay 103 as shown in FIG. 1 and as described before. That is, missing or corrupted packets from base stream 222 may be replaced or supplemented by using the corresponding packets received earlier from staggercast stream 211. Thus, a quality of service (QoS) to a user of the staggercast communication system may be maintained and decoder 204 is able to provide a more robust or error resistant decoded stream 224.